IN THE LANGUAGE OF DOTS AND DASHES

It’s tempting to assemble a simple Telegraph device and to communicate using Morse code. Reliable two-way communication is needed in the conduct of military sports games and competitions, in a tourist campaign and in summer camp, it is interesting to set it up at home or at the cottage.

Two identical apparatus are connected via the terminals X1, x2 and X1¹, x2¹ two-wire communication line. Moreover, a wire can not be isolated. If the device you intend to use to communicate in an apartment or with a friend living next door, enough to hold only a single wire, and the second will serve you metal pipes of heating or water supply (Fig. 1).

 

Schematic diagram of the apparatus signal-calling devices presented in figure 2. They provide adequate volume, feeding on only one element At 1.5 V (“316”, “332”, “373”), “Heart” of each unit — stand-low-frequency oscillator assembled on two galvanically connected transistors V2, VЗ different structures according to the scheme of asymmetric мультиdибратора-the one-shot. Load is dynamic head B1.

Positive feedback through the capacitor C1. Standby vehicles provided by the bias voltage supplied from the power sources G1 and C1¹ via the resistors R5 and R4 (R5¹ and R4¹) on the bases of both transistors — V2 (V2¹) is negative and VЗ (VЗ¹) positive polarity.

 

 

Fig. 1. The inclusion of machines in the line.

 

 

Fig. 2. Schematic diagram of the telephone device.

 

Switch S1 is set in position “welcome” transistors are closed dynamic head B1 (B1¹) is disconnected from the power sources, generators do not work. Current consumption is so small that is almost comparable with the self discharge current of the galvanic cell through its own internal resistance.

 

The principle of two-way communication based on the remote start standby generators NCH. When you need to call the person on the other end, you briefly push the S1 button “Call” your device. Through closed contact and through a resistor R3 to the base of your device V2 receives a positive bias voltage, and the generator is excited. Dynamic head B1 will reproduce the tone. Duplication of call is necessary for auditory control its transmission and turn the health of the machine.

 

At the same time, sending the call in the direction of the correspondent, and you create a positive bias on the base of the transistor V21 of the second apparatus. It arises through the circuit: +G1¹, wire connecting terminals x2, x2¹, contact button S1, the forward resistance of the diode V1, the wire between the terminals X1, X1¹, the total resistance of the resistors R1¹ R2¹, the contact button S1¹ and, finally, the base of transistor V2¹. At this time, the device works the point B, and your partner hears the ringtone.

When he stops, receives a return signal. The chain in its passage similar to the previous one. Thus, pressing the button of your machine, you control and operation of the apparatus at the opposite end of the line.

 

It is clear that the value of resistance of the connecting line (depending on the length, cross section and material of the wire) will significantly affect the mode of excitation of the generators. To compensate for this effect the resistor R2 (R2¹), which together with the diodes V1 (V1¹) perform the function of current distribution. Therefore, before to connect the devices to the line, the sliders of variable resistors set to the rightmost position according to the diagram (maximum resistance). Then, taking cues partner, set using the variable resistor of the device the maximum volume and the most pleasant tones. The same setting is carried out at the opposite end of the link. The apparatus is ready for operation.

 

 

Fig. 3. Wiring diagram of the apparatus.

 

You can include in the overall and 3-4 of the machine. However, it must be borne in mind that the difference in the resistances of the lines should not exceed 1 -2 ohms.

 

And now about the design and details of the device. Dynamic head, button and variable resistor mounted on the front panel of a small-sized transistor radio. In this place the mounting plate (Fig. 3) made of foil Micarta or fiberglass with a thickness of 1,5—2 mm, and a galvanic cell. Clamps for connecting communication lines of any type, it is mounted on the side wall of the housing.

 

In a Telegraph device, you can use transistors series КТ306, КТ342, KT315 (n-p-n) and МП39-МП42 (p-n-p) with gain h₂₁3≥30 and preferably with a small current Ikbo ; diode type D2, D9, D20. Constant resistors — MLT-0,5, variables of any type with a resistance of 5.1 to 10 kω. Microswitches — MPZ, МП7 or the like. Dynamic head is calculated for a power of 0.1—0.25 W , has a voice coil resistance of 6-10 Ohms.

 

E. SAWICKI, Korosten, Zhytomyr region.